Differences in oxidative status explain variation in thermal acclimation capacity between individual mosquitofish (Gambusia holbrooki)

1. Evolutionary theory predicts that the capacity to acclimate should be favoured in variable environments. However, perfect compensation for thermal variation is rare and the capacity for thermal acclimation can vary considerably between individuals within natural populations. This variation may be explained by costs associated with acclimation, but it is not clear what these costs are.
2. We tested the hypothesis that oxidative stress is a cost of acclimation that could explain the variation between individuals in acclimation capacity. We acclimated individual mosquitofish (Gambusia holbrooki, n = 416) to 18oC and 28oC sequentially, and determined swimming performance at each temperature to evaluate their acclimation capacity. Fish were then acclimated to either cold (18oC) or warm (28oC) conditions, and we increased antioxidant capacities of a subset of fish experimentally by administering N-acetyl cysteine (NAC). We measured H2O2 production, catalase antioxidant activities, and oxid...